XRF 241001A/SN 2024aiiq: A faint soft X-ray transient detected by SVOM with a broad-line type Ic supernova revealed by JWST

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Context. X-ray flashes (XRFs) are a type of gamma-ray burst (GRB) with prompt emission predominantly below ∼30 keV and have been poorly detected by previous missions monitoring the high-energy sky. The advent of the Space-based multiband astronomical Variable Objects Monitor (SVOM), with its wide-field instrument ECLAIRs, provides a new way to detect soft X-ray transients such as XRFs, complemented by rapid onboard multiwavelength follow-up. Aims. We present photometric and spectroscopic observations of XRF 241001A detected by SVOM, a soft, subluminous, and low-energetic burst located in a poorly populated region of the Amati relation. We investigated the origin of its faint, soft high-energy emission to assess its connection to the long GRB population. Methods. We analyzed the SVOM/ECLAIRs prompt emission and modeled its afterglow emission from X-ray-to-radio. We present JWST /NIRSpec and SVOM/VT observations of the associated supernova (SN 2024aiiq), which we modeled with an Arnett radioactive decay component, and we compared its properties with previously detected GRB/SNe. Results. The event XRF 241001A is located at z = 0.573 and has a prompt emission dominated by photons below 20 keV, with a duration of T 90 = 3.14 seconds. Its spectrum is consistent with both thermal and nonthermal models, each implying a low E peak < 10 keV and E iso ∼ 8 × 10 49 erg. The X-ray-to-radio afterglow modeling favors an origin from a relativistic jet viewed on-axis and supports a nonthermal origin of the prompt emission. In the optical, XRF 241001A exhibits an early blue emission, similar to that detected in some extragalactic fast X-ray transients (eFXTs) and inconsistent with the expected synchrotron emission from a relativistic jet. The JWST /NIRSpec observations firmly established its collapsar origin by revealing an SN Type Ic with broad lines, comparable to SN 1998bw and SN 2025kg-like events near maximum light and with similar properties. Conclusions. The event XRF 241001A is a soft low-luminosity collapsar event produced by a weak relativistic jet observed on-axis, supporting the view that at least part of the XRF population forms the low-energy soft tail of the long GRB population. Its observation demonstrates the potential of SVOM/ECLAIRs to probe the soft regime of the high-energy transient population that remains largely unexplored.